HYERES (83) 27.05.2016

On 27 May 2016 at 16:26, a witness lying on the Plage des Salins in Hyères (83) was puzzled by a phenomenon in a sky crossed by an aircraft condensation trail. He described a straight black or very dark gray shape, like a curtain of smoke, visible from the ground up into the sky. It was stationary, and he heard no particular sound. He filmed it. Only 1 account was collected. GEIPAN's analysis of the account, photographs and video attributes the unusual appearance to a natural phenomenon it calls a volumetric shadow viewed edge-on, or an edge shadow. It explains that this becomes visible when a straight aircraft contrail passes in front of the Sun and the Sun, trail and observer align. A shadow then extends through the volume of atmosphere within the thin plane defined by the trail, observer and Sun; see the investigation report. GEIPAN compares this layer of atmosphere to a slightly tinted pane of glass: unobtrusive viewed face-on, but appearing as a dark line when viewed along its edge. The longer the pane, or here the straight portion of the contrail, the darker the line. If the observer is outside that plane, the dark appearance and the phenomenon disappear. The effect therefore requires particular conditions, all present for this witness. The dark line extends across the full vertical extent of the witness's view, including the sky. GEIPAN notes that someone who sees the contrail might readily imagine its ordinary shadow on the ground, but find a shadow in the sky much less intuitive. GEIPAN classifies the case as A: an aircraft contrail producing a volumetric shadow viewed edge-on.